The invention relates to a process for the production of bodies, especially building units from afterhardening materials containing hydraulic binder, particularly cement as setting agent.
Such building unit production methods are known, at which hardening of the cement-set moulded material is accelerated by injection of CO.sub.2 gas into the raw mixture (e.g. U.S. Pat. No. 4,093,690. These methods are based on carbonation, i.e. a process when the large amount of Ca(OH).sub.2 compound present in the cement mortar quickly changes over to limestone upon the effect of CO.sub.2 gas. The limestone molecules being formed during this process, become so tightly bonded to each other that the product, e.g. building panel may reach even 35-50% of its 28-day-strength in 5-30 minutes, though hydration of the binding material, e.g. cement has not even begun.
The carbonation takes places generally in a closed space containing the raw mixture to be set with cement by producing differential pressure, then a pressure exceeding the atmospheric one is brought about with the injection of CO.sub.2 gas, as a result of which the CO.sub.2 gas may penetrate into the pores of the raw mixture and chemical reaction takes place. The raw mixture is filled into a mould determining the shape of the product to be produced and compacted, then placed into a closed space together with, or removed from the mould. These methods, however, are fairly costly, because the closed spaces require careful sealing to be realized with difficulty and at high cost. Apart from this, the alternating use of vacuum and high pressure is lengthy, thus, the techologies allowing only a step by step production carried out with several operations (filling into the mould and compacting; filling and discharging the carbonation space; carbonation) take fairly long time.
A building unit production technology combined with carbonation is described in the Hungarian patent specification No. 189.455 where elastic fibrous material as additive is used for the preparation of the cement-set raw mixture, and there is utilized the characteristic feature of this mixture for more or less elastic reversion after compaction, thus, its volume expands when the compressive force is stopped during the setting time of the hydraulic binding material, i.e. cement. The raw mixture placed between two press-plates is compressed in a greater degree in the vicinity along their flanges than the rest of the mixture--either by using a thicker part along the flanges of the press-plate or by applying a locally greater amount of raw mixture--thus, a strip of higher density, consequently of lower gas permeability is formed at the flanges, than within. This strip of higher density along the flanges functions as a seal, and prevents the CO.sub.2 gas injected for carbonation from escaping from the mixture on the sides. Although this method is more favourable than the former ones its drawback resides firstly in its periodicity, thus in its relatively low productivity and in the fact that a solid end-product can be produced only from mixtures containing elastic fibrous material.
The invention aims at providing a process for the production of bodies, particularly building units from an afterhardening material by accelerating the setting with carbonation, which partly allows a continuous production thereby considerably improving the productivity and economic efficiency, and partly it is not restricted to the use of afterhardening mixtures prepared with an elastic fibrous additive as a starting material (to be moulded), whereby it substantially extends the choice of products to be economically produced with carbonation.
The invention is based on the recognition that when the afterhardening material is passed through a moulding space open at both ends, and escape of the CO.sub.2 gas is prevented by a continuous mechanical compaction of the raw mixture in the vicinity of the point of inlet and by reducing the pressure of the CO.sub.2 gas to a minimum--in the given case to the atmospheric pressure--in the vicinity of the point of outlet, and the CO.sub.2 gas is injected between these two points into the mould space evenly distributed along the mould face(s), however under a pressure reduceed from the inlet towards the outlet, the production may be made continuous, and the product emerging from the mould space will appear in a solid, moulded state as a result of carbonation taking place in the mould space.
On the basis of this recognition, the problem was solved by a process according to the invention, in the course of which the still not hardened mixture is admitted into the mould, where carbonation reaction is brought about by injection of CO.sub.2 gas into the mixture, and thereby the mixture is hardened, said process comprising the steps of pressing the afterhardening mixture continuously through the mould space open at both ends, while CO.sub.2 gas is injected into the material under pressure reducing from inlet port of the material toward the outlet port of the hardened body, and creating a quasi gastight layer from the afterhardening material with mechanical compaction in this mould space in the vicinity of the inlet port and bringing about a quasi-gastight condition between this layer and the mould surfaces, and in the vicinity of the outlet port injecting as much amount of CO.sub.2 gas into the mould space as necessary for the complete, or essentially complete chemical reaction of carbonation. The afterhardening material is stamped-pressed into the mould space preferably with a reciprocating device.
Expediently, the CO.sub.2 gas is injected into the mould space through at least one of the confining surfaces under pressure exceeding the atmospheric pressure; and when passed through the afterhardening material the gas of reduced pressure and quantity is discharged from the mould space through at least another mould face, and/or vacuum is applied to at least one face of the mould space, and this way the CO.sub.2 gas is made flown through the material, or its flow is intensified.
According to another advantegeous feature of the invention, in a zone following the compacted layer of material in the vicinity of the inlet port, CO.sub.2 gas at a pressure of suitably 3-6 bar is injected into the pores of the mixture then--looking in the direction of the material's movement--in a second zone, where the instantaneous explosion-like reaction of carbonation takes place, CO.sub.2 gas under a lower pressure of e.g. 2-3 bar is injected into the material, the quantity of which is essentially the same as that of the CO.sub.2 gas consumed by the reaction, whereby the carbonation reaction is continued, then in a third zone CO.sub.2 gas under even lower pressure of e.g. 1-2 bar is injected into the mould space, whereby essentially full completion of the carbonation reaction is realized. A further embodiment of the process is characterized by creating a balancing zone in the mould space situated directly behind the outlet port of the material hardened by carbonation, where the gas outflow is checked, and in the zone(s) behind the balancing zone, gas is injected as a function of the quantity of the outflowing amount and/or pressure of the gas. It is generally advisable to cut to size--suitably by sawing--the carbonation-hardened body leaving the mould space, and to inject the CO.sub.2 gas into the mould space with a gas mixture, containing suitably at least 30% of CO.sub.2 gas.
It may be advisable to inject the CO.sub.2 gas into the raw mixture prior to feeding it into the mould. The setting process can be accelerated by this carbonation pretreatment.
The apparatus according to the invention contains a mould, a CO.sub.2 gas-source, e.g. gas bottle and openings e.g. holes in at least one wall of the mould, suitable for injection of CO.sub.2 gas into the mould space, the pressure of which exceeds the atmospheric pressure, and this apparatus is characterized in that the mould has an inlet port for feeding in the raw afterhardening mixture and an outlet port for discharging the body hardened by carbonation; a press mechanism situated in front of the inlet port for pressing the raw afterhardening mixture into the mould space, and moving the afterhardening mixture and the body hardened therefrom by carbonation through the mould space; and the holes leading into this mould space and used for injection of the CO.sub.2 gas are divided into separate hole groups communicating with devices suitable for injecting CO.sub.2 gas, at pressures to be separately controlled for each zone. It is expedient when at least one wall of the mould is provided with holes for outlet of the CO.sub.2 gas remaining--in given case--after the completed chemical reaction of carbonation, which holes are expediently communicating with pipes connecting the CO.sub.2 gas source, e.g. gas bottle with the mould plate containing the holes for injecting CO.sub.2 gas into the mould space.
An embodiment of the apparatus is characterized by having a forward pipe for feeding the CO.sub.2 gas into the mould space and a return pipe for feeding back into the forward pipe the CO.sub.2 gas remaining--in a given case--after the completed carbonation reaction; a gas pump being connected to the forward pipe into which also the return pipe is leading, and--in up-stream direction of the gas flow--a pipe containing shut-off means, leading out of the CO.sub.2 gas supply source, e.g. gas bottle being joint to the return pipe before the pump, and the forward pipe being interconnected through leg pipes containing valves with separate hole groups on the gas inlet side, while leg pipes containing similarly valves and leading from the hole groups into the return pipe are provided for discharging the gas remaining--in a given case--after the completed carbonation reaction. A vacuum pump can be inserted into the return pipe.
According to a further feature of the invention the hole groups on both the gas inlet side and the remaining gas outlet side is leading into separate closed chambers fitted expediently gastight to the outer face of the mould plates. Furthermore it may be of advantage, when the hole groups are leading from--e.g. meandering--ducts running inside the mould plates into the mould space, each duct communicating with one of the leg pipes emerging from the forward pipe or with one of the leg pipes leading into the return pipe.
According to another embodiment of the apparatus given by way of example, a device, e.g. a saw suitable for cutting up the carbonation-hardened body emerging from the mould space is arranged behind the outlet port of the mould.
According to another arrangement of the invention, chambers covering at least one of the hole groups are fitted to the outer side of the mould plates in the vicinity behind the outlet port of the mould, and gas outlet stubs containing control valves are leading out of the chambers.
A further embodiment of the apparatus is characterized by providing a press mechanism with a reciprocating beater, e.g. a piston, the cross sectional shape and size of which are the same or essentially the same as those of the mould's inlet port. In this case it is expedient, when the position of the mould and the path of the piston are vertical, the piston is fitted between guide rails, the guide rails are covered by a bell-shaped protective cover, the lower flange of which is running in the vicinity of the lower edge of the guide rails and a gap is provided for between said lower flange and the guide rails; and the actuating mechanism together with the protective cover is situated in a hopper serving for feeding the raw afterhardening mixture into the mould, the hopper leading into the upper end of the mould space.